End effector mechanisms refer to the portion of a surgical instrument that contacts and manipulates tissue in a patient. Prior art end effectors include grasping forceps, which grasp but do not intentionally cut or puncture tissue. These devices replace the surgeon's hands in the traditional open surgery. However, prior grasping devices often cause problems due to their inability to properly grasp an object. The lack of satisfactory holding power of these instruments can complicate the surgeon's work. Tissue that must be manipulated during a surgical procedure can have widely varying shapes or surface characteristics and can be highly slippery and difficult to grasp. Additionally, such prior devices lack the necessary holding power, thereby forcing the physician to exert significant grasping pressure in order to manipulate tissue as required to perform the surgical procedure. Use of such high grasping pressures can result in increased long-term trauma to the tissue.
Referring to FIG. 2, a typical surgical instrument 25 has a hollow cylindrical shaft 32, which includes a solid actuating rod (not shown). The rod is connected at the distal end to the effector mechanism 31 and at the proximal end to one member of the handle assembly 30. When the handle is operated, the rod slides through the shaft and actuates the end effector mechanism. Serrations and other features enable the end effector to perform various surgical functions, such as gripping or cutting.
Many creative linkages have been devised for converting the surgeon's manual efforts, at the handle end of the instrument, into opening and closing of the instrument's jaws. Typically, the handle assembly 30 has a stationary member 35 rigidly joined to a hollow shaft 32 and a movable member 34 pivotally joined (with pivot pin 33) to an actuator rod that is mounted and is capable of reciprocal movement within the shaft. When the surgeon squeezes the stationary and movable handle members together, the actuating rod acts upon the jaws in such a way as to make the jaws close. When the surgeon spreads the stationary and movable members apart, the movements are reversed and the jaws open.
In many prior art instruments the end effector mechanism 31 includes upper and a lower elongated jaw components 45, 46, pivotally connected to each other and to the shaft 32 and actuator rod with pivot pin 90. When operating the jaws 45, 46 of a typical instrument, surgeons have experienced difficulty in grasping slippery tissues because the jaws close first at their rear ends, and thereby tend to propel or push the tissues out from between the jaws, as illustrated in FIG. 1A. Consequently, trauma of the tissue may result from repeated and increasingly aggressive attempts to grasp the tissue.
U.S. Pat. No. 6,238,414 describes a surgical instrument that addresses the problem of grasping a large cylindrical object by keeping the opening jaws parallel to each other, as shown in FIG. 1B, FIG. 2A and FIG. 2B. However, this jaw arrangement is not always optimal for grasping a large object, especially one that is not cylindrically shaped. Accordingly, there is a need for improved end effector mechanisms that provide optimal grasping of large objects of any shape.